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Teardown of Kentli PH5 1.5 V Li-Ion AA battery

After having an entire month of dormancy on this blog, I’m finally beginning to cross off the blog posts on my “Pending” list.

Last year, I made a blog post talking about Kentli’s lithium-ion based AA battery that has an internal 1.5 volt regulator. The first order never arrived, and the second one had arrived a few months ago but I never got to actually taking one of the cells apart. That changes today.

Cell overview

The battery itself looks like a regular AA battery, except for the top positive terminal. There’s the familiar ‘nub’ that constitutes the 1.5 volt output, but also has a recessed ring around it that provides a direct connection to the Li-ion cell’s positive connection for charging.

Label of cell

Ditto, with cameo appearance of MAX3232 to prevent the battery from rolling off my desk…

Top of battery with 1.5 and Li-ion cell terminals

After peeling the label, we are met with a plain steel case, save for the end cap that appears to be laser spot-welded. Wanting to take apart the cell with minimal risk of shorting something out inside, I used a small pipe cutter to gently break apart the welded seam. Two revolutions and a satisfying pop sound later, the battery’s guts are revealed.

Label mostly removed – note seam on top right

Pop goes the weasel, er, battery

Battery internals

Kentli branding on flex PCB

Label of Li-ion polymer cell

Flex PCB soldered to end cap circuitry

The other, less interesting end.

The PCB that holds the 1.5 volt regulator is inside the end cap, with the rest made up of the Li-ion cell itself. Curiously enough, the cell inside is labeled “PE13430 14F16 2.66wh” which is interesting in more than one way. First of all, the rated energy content of the cell is less than what’s on the outside label (2.66 watt-hours versus 2.8), and the cell inside is actually a Li-ion polymer (sometimes called a “Li-Po” cell) type; I was expecting a standard cylindrical cell inside. Unfortunately, my Google-fu was unable to pull up any data on the cell. I might attempt to do a chemistry identification cycle on the cell and see if TI’s battery database can bring something up.

Battery circuitry

Close-up of end cap circuitry

Ditto, with XM5232 markings visible. Lens flare abound!

The end cap’s PCB uses a Xysemi XM5232 2.5 A, 1.5 MHz synchronous buck converter to provide the 1.5 volt output. According to the datasheet, it is a fully integrated converter with all the power semiconductor components residing on the chip itself. The converter is rated for 2.5-5.5 volt operation, well within the range of a Li-ion cell. Additionally, it has a rated Iq (quiescent/no-load current) of only 20 microamps. The buck converter’s 2.2 microhenry inductor is magnetically unshielded which may cause some increased EMI (electromagnetic interference) emissions, but I don’t have the equipment to test this.

Protection circuit with XB6366A IC markings visible

I was looking around for the battery’s protection circuit, and found it on the flex PCB that surrounds the Li-ion cell. It uses a Xysemi XB6366A protection circuit which, like the buck converter, is a fully-integrated device; there are no external protection MOSFETs for disconnecting the cell from the rest of the circuit.

32 thoughts on “Teardown of Kentli PH5 1.5 V Li-Ion AA battery”

I’ve just followed a trail around the interwebs looking for a usable lithium, rechargeable battery for my Anywhere Mouse MX. I’m looking for good reasons not to invest. I found myself on this page today, having read your posts on another forum, and note that it is dated yesterday! What are the chances, I wonder…

In any case, I wait with bated breath for your conclusion on the performance of these cells, on which I’ll base my decision to invest in a set plus charger for use with wireless computer mouses.

Obviously I’d appreciate it if you’d complete your testing in less than a year! Next week is fine with me.

Please replace prior post with this one. Only difference is the “notify me” flag is set.

I do like “techo” things, BUT have to ask, ‘What is the point of this cell – apart from “being fun”?’. Existing or slightly greater capacity name-brand NimH with equal or longer cycle lives are readily available. NimH charge time can be 1 hour with standard chargers. LiIon chemistries take several hours except in very special cases, with typically 80% in one hour.
Discharge rates of NimH can be over 4C fully charged and say 2C continuous. The discharge rate of this cell is limited by the capabilities of the buck converter.
Overall it appears a tour de force of technology but apart from that it’s not obvious why one would be useful

I think the goal of this battery is trying to shoehorn a Li-ion cell in applications that typically cannot use a battery with such a high terminal voltage. Its energy density, if the labeling is truthful, is comparable to a modestly-sized AA Ni-MH cell (such as a ~2000 mAh or 2400 mWh Eneloop), but with significantly less weight even with the use of a buck converter to create the 1.5 volt output.

Preliminary testing shows that the buck converter can supply up to roughly 2 amps of output current, which is far less than the current that a Ni-MH cell can deliver; however, there is also a difference in terminal voltage (nominal 1.5 versus 1.2 volts) and the ‘flatness’ of the output voltage over the discharge cycle.

Personally, I haven’t found much use for these batteries. Most of the applications I use won’t take advantage of the constant-voltage output of this battery, or they use so little current that alkaline or lithium primary batteries would make more sense (no buck converter is used which avoids the issue of quiescent current draw). Coupled with its high cost ($10-15 per cell is a really hefty price for a battery, regardless of the technology inside), I doubt these will really take off in the consumer market.

I find this cell interested as I intend to use it in my Garmin GPS receiver for mountain hiking. Here weight reduction becomes vital. The device normally uses two AA cells. The lightest batteries available for this is a Lithium type from Energiser. It weights only 16 grams apiece but it is not rechargable, a type I greatly oppose for environmental reasons. The rechargable NiMH I used in my Garmin previously weigh 26 gram apiece and last less than three hours. These new Lithium cells weigh only 19 grams apiece.

I think part (or most) of the attractiveness of a cell like this might be in the low self-discharge rate compared with NiMH cells. But: 1. Everything depends on management, it MUST disconnect the cell when not in use. And 2. Applications where you need low self discharge are typically very low current long-term applications, and these switching regulators are typically not very efficient at very low current draw. Where this might make sense is in an application where you need a lot of current from a AA battery on-demand, but where the demand is very infrequent. Gimmick? Maybe… Anyway, it’s hard to shoe-horn this battery into any sort of application slot without knowing how it actually performs. I look forward to that post.

High-current, infrequent usage is absolutely the scenario. Flashlights, electric razors, digital cameras, etc.. Low self-discharge, no memory effect, and fast charging are all pretty compelling for these.
Consumer appliances/devices are increasingly adopting non-user-replaceable internal li-ion batteries or (expensive) proprietary li-ion battery packs instead of standardized AA/AAA batteries. There are good reasons for that shift. But it’s a problem. It’s expensive and difficult to replace those batteries, and that contributes to the “planned obsolescence” of those appliances/devices.
I’d love to see a return to standardized commodity batteries – at least in cases where it’s practical to offer user-replaceable batteries. AA isn’t an ideal standard for lithium-ion rechargeable batteries, but it’s a good place to start. If these guys are able to (a) lower the the price to more competitive levels (~$2/battery is current market price for NiMH rechargeables; I could see these selling for $3-$4 but not the current $10) and (b) either improve their distribution or license their patent to a battery company with wide distribution, then these could breathe new life into existing electronics that depend on AA. That might be enough to raise consumer expectations for standardized, user-replaceable batteries enough to reverse this trend … and maybe even attract enough interest to push a new battery standard that makes more sense for rechargeable li-ion polymer than AA.

They make 3.7V Li-ion batteries in roughly a AA form factor without the weirdness of this cell to make it work in a 1.5V application. It would be nice if those were more common, but there’s usually a trade-off between replaceability and size.

I have an Arjo lift that needs new battery NDA-0100-20 24vdc 4aH
I will crack it open and install solder a bunch o series/par’ll batt’s
I love my 9yo Lithium Ion screwdriver, where can I buy reasonable, Canada
or do i need to get technical…duty charging cycle doh
in which case $tore NiMh AA x 40 = $50

The NDA 0100-20 battery is a 4Ah sealed lead-acid (SLA) battery. Apart from that, I don’t have any more information on them, but I am sure that you will find two fairly standard 12V lead-acid batteries inside the casing.

If you’re trying to buy a new Li-ion based screwdriver, I don’t have any specific place to look for. If you want to refurbish it with a new Li-ion battery, look up the battery’s part number (for example, it might be using an INR18650 cell) and buy a version that has solder tabs installed.

A watthour is not the same as an amp hour. The kentli batteries are rated in watt hours, not amp hours. Watt hours = amp hours x voltage. Since the internal cell is rated at only 2.66whrs, the rating of the kentli cell is exaggerated. A little power is lost due to conversion inefficiencies too.

you wrote :
” The buck converter’s 2.2 microhenry inductor is magnetically unshielded which may cause some increased EMI (electromagnetic interference) emissions, but I don’t have the equipment to test this.”
look at the comment of
Nathan Hardenburg (https://www.youtube.com/watch?v=nXGN0ZJxGQg), seems you’re right:
“I bought a set of 4 plus charger, for the sole reason of using with my TECSUN PL-310et, on AM, which is what I use, it creates TONS of noise, totally unlistenable..I tried them on another small digital AM/FM/SW radio, and it was the same thing. These are unsuitable for AM radio, that they have a patent on something as failed as this, is retarded.﻿”

I can see application in transmitting devices which are not designed to take 1.2v NiMH input. Examples are wireless mics. As long as EMI is not an issue of course, which is yet to be seen. These devices tend to either not work at all or work for a very short period of time, or have drastically-reduced transmission distances. Another application I can see is some cheap children’s toys these days which struggle with the low voltage of NiMH’s.

Primary use I see for these cells is for flashlights/headlamps.. I use a Petzl Duo for caving, which comprises an LED module for proximity lighting and a Halogen bulb for spotting. NiMH runs the LED module satisfactorily but is positively anaemic for the Halogen. Conceivably the Kentli cell would make the Halogen perform. Alternatively I could just get the dedicated Petzl ACCU rechargeable battery pack to run the unit!!

I use these batteries for an electric catflap with RFID sensing, and an Apple mouse which is a power hungry beast (eats two AA in 5-6 weeks or so), and it doesn’t like NiCD or NiMH 1.2 volt cells. These Kentli cells work fairly OK, sometimes the Bluetooth connection is lost which must be due to the RF noise that it generates.

However a worse issue is that there does not seem to be a cell protection against full discharge. The Apple mouse will complain about low voltage, but the catflap will keep on draining the battery until I find out that all of my cats have been (forcibly) sleeping outside. The cell is discharged to 0.002 volts, which is absolutely unhealthy for LiPo chemistry and will certainly destroy it after a couple of times. That really is a big design issue.

There is Li-ion battery protection present (it uses an XB6366A integrated protector that combines the control and switching elements); once the Li-ion battery voltage drops below 2.4 volts, the XB6366A will turn off an internal MOSFET switch and subsequently stop any further discharge activity. This does have the effect that the battery appears to be at 0 volts when measuring across the external terminals.

Still, 2.4 volts is unhealthily low especially at low discharge rates, since Li-ion batteries should not be discharged below 3 volts in order to preserve cycle life/endurance. Most Li-ion protectors cut off at this low voltage since the battery voltage sags easily at a low state-of-charge, due to the increased internal resistance inside the battery. However, if the protection MOSFET is shorted for some reason, that’s a pretty big safety issue since that means the protection functionality is lost.

The manufacturer of the battery has other models of Li-ion AA batteries that drop the DC-DC’s output voltage as the battery’s charge depletes, simulating a low-battery voltage condition. They carry the PK5 and PM5 models – however, I have not tested them so I do not know how well they would necessarily perform compared to the PH5. I wonder if they will send me some samples if I ask them…

Have you seen any info about the acceptable temperature operating range? I have two use cases… one involves lower temps… say 0-32 deg F for a few hours in a light. The other is with camera flashes… the batteries might sit for a while but when I need them I’d really like them to work without recharge… but then the concern is the temperature at higher draw.

I have not seen any significant information about the minimum/maximum operating temperature of these batteries, but I imagine they would largely be dictated by the characteristics of the Li-ion cell itself. As with all batteries, they will experience reduced performance in cold weather (their internal resistance increases, reducing effective capacity and ability to supply high currents). Camera flashes have very “bursty” load characteristics which will put significant strain on the batteries but may not necessarily have the same heating effects as a high-current constant load, such as a flashlight.

I use a lot of trail cameras (outdoor wildlife motion camera) that require AAs. I use Energizer Lithiums because as time goes on the night flash range is not decreased nand they work well in hot and cold temps. NiHM is great (Eneloop Pros) and cost effective, but lasts 1/2 the time when the cameras are in hot summer weather.

Use a wildlife camera around my property and after a AA battery that has a stable voltage. Alkaline batteries once they drop below 1.3v dont have enough power for the infra red LEDs to work. Nicad and NiMh voltage at 1.2 volt isn’t enough also. Am considering these. Would like to see a voltage current drain comparison between the Lithium and alkaline AA batteries

The recessed ring terminal on the positive end of the battery can be used to charge the Kentli batteries with a regular Li-Ion charger.

I have some thick copper bus wire for solar panels that I curled into a ring that fits into that recessed terminal. Using that, I can charge the Kentli batteries with my Nitecore Intellicharger i4 without issue.